Heart Monitoring Device

ABSTRACT

An implantable heart stimulating device for indicating congestive heart failure (CHF) has a processor and a sensor combination that senses at least two heart events during one heart cycle at different locations of the heart. The processor is supplied with signals from the sensor combination relating to the sensed events, and determines therefrom at least one heart time interval between the sensed events in the same heart cycle. The processor determines a CHF indicator value representing a degree of CHF based on a variability measure calculated from at least two heart time intervals from at least two different heart cycles. The processor determines the CHF indicator value in relation to previous CHF indicator values.

FIELD OF THE INVENTION

The present invention relates to a heart monitoring device according to the preamble of the independent claim and in particular to a new way to measure and quantify the degree of congestive heart failure. A determined congestive heart failure indicator value—alone or together with other metrics—may advantageously be used in assessing the patient's status, titrating drugs and/or evaluating therapy.

The invention may be applied to all dual chamber devices, preferably biventricular devices, implanted for the treatment of CHF. No specialized leads or hardware is required. The invention is also applicable by using a conventional ECG equipment provided with surface electrodes.

BACKGROUND OF THE INVENTION

Approximately 23 million people worldwide are afflicted with congestive heart failure (CHF), and 2 million new cases of CHF are diagnosed each year worldwide. In contrast to other cardiovascular disorders that have actually declined during the past few decades, the incidence of heart failure is one that rises. It is, in fact, the most rapidly growing cardiovascular disorder in the United States.

Congestive heart failure is a chronic inability of the heart to maintain an adequate output of blood from one or both ventricles of the heart to meet the metabolic demands of the tissues. With a markedly weakened left ventricle or right ventricle or both, the volume of blood presented to the heart is in excess of the heart's capacity to move it along. Consequently, fluid builds up behind the heart. With a weakened left ventricle or right ventricle or both, there is a shift of large volumes of blood from the systemic circulation into the pulmonary (lung) circulation. If the inability to move the volume of blood forward is due to a left heart side problem without the right side falling as well, blood continues to be pumped into the lungs by the normal right heart side, while it is not pumped adequately out of the lungs by the left heart side. As the volume of blood in the lungs increases, the pulmonary vessels enlarge, pulmonary venous congestion develops, and, once the pulmonary capillary pressure rises above a critical point, fluid begins to filter out of the capillaries into the interstitial spaces and alveoli (air sacs in the lungs where exchange of oxygen and carbon dioxide occurs), resulting in pulmonary oedema. Subsequently this can lead to pleural effusion (effusion is the escape of fluid into a part) and abdominal effusion. If the abnormality lies in the right heart side or the pulmonary arteries, limiting the ability to move blood forward, then congestion occurs behind the right heart side (causing pleural effusion and/or build up of fluid in the abdomen).

Although advances in pharmacology have led to better treatment, 50% of the patients with the most advanced stage of heart failure die within a year. Typically, heart failure patients receive several chronic oral therapies, including diuretics, ACE inhibitors, beta-blockers and inotropic agents.

A majority of patients are treated with drug therapy, but for patients with advanced CHF, device-based therapy or transplantation are their only alternatives. A large number of patients with advanced CHF have received left ventricular assist devices, and a number of promising technologies, including biventricular pacing and defibrillators and ventricular assist devices represent growing fields.

U.S. Pat. No. 6,763,267 relates to a ventricular conduction delay trending system and method for ascertaining the condition of the heart's conduction system in a patient treated for congestive heart failure with pacing therapy. Ventricular activation patterns are monitored over time in order to detect changes in the heart's conduction system that may occur due to physiological regeneration of conduction pathways. The activation patterns are reflected by electrogram signals detected from different ventricular locations during one heart cycle. By measuring the difference in conduction times of an excitation impulse travelling from the AV node to the different ventricular locations, a parameter representative of the heart's conduction system is obtained that may be used to adjust the pacing therapy in accordance therewith.

The present invention is based upon the well-known fact that the heart rate variability decreases as CHF worsens. One reason to this may be decreased autonomic control and it has been found to correlate well with the degree of heart failure.

The inventor has found that patients suffering from CHF not only have a decreased heart rate variability, but also a decreased variability of the atrio-ventricular conduction time is affected, as it is controlled in the same way. The variability, in particular the standard deviation, of the intrinsic atrio-ventricular conduction times were analyzed for nine CHF patients and found to be lower than in a control group of patients not suffering from CHF.

Thus, the object of the present invention is to achieve an improved heart stimulating device for monitoring congestive heart failure.

SUMMARY OF THE INVENTION

The above-mentioned object is achieved by the present invention according to the independent claim.

Preferred embodiments are set forth in the dependent claims.

According to a preferred embodiment of the present invention the intrinsic PR interval is regularly measured for a predetermined period of time in order to assess its variability. This is done typically once a day, preferably when the patient is at rest.

The variability measures—or a linear or non-linear combination of them—may be stored in the memory of the device to form a trend. This trend may later be displayed to the physician at the time of follow-up.

As mentioned above, the variability of the PR intervals is related to the neural control of the heart rhythm. Low heart rate variability (i.e. variability of the time between heart beats, e.g. consecutive heart beats) have been showed to correlate to the degree of illness and the same have been found with regard to PR interval variability.

If a patient has atrial asystole, i.e. the automaticity of the atria is extremely low and atrial pacing is present for nearly 100% of the time, the PR interval is impossible to measure as there are no P waves. In that case, or in other cases when atrial pacing is very important, the variability of the AR interval may be used instead of the PR interval.

The present invention may be used in implantable devices provided with one atrial electrode and at least one ventricular electrode, i.e. both dual-chamber and biventricular devices, the time from the P wave to the first or second electrode, or both of them, may be used to perform the variability calculations.

According to an alternative embodiment the present invention is instead implemented in a conventional ECG equipment provided with surface electrodes.

Herein the expression variability is to be interpreted in its broadest sense, i.e. denoting the degree of changes or variations of a predetermined entity from time to time.

The measures of variability of the PR intervals or other intervals may include the standard deviation, the range (i.e. max value-min value), SDNN (the mean of the standard deviation of e.g. 5 minute periods) etc. The invention is not limited to the use of just these measures.

SHORT DESCRIPTION OF THE APPENDED DRAWINGS

FIG. 1 shows a schematic block diagram illustrating a preferred embodiment of the present invention.

FIG. 2 shows a flow chart illustrating essential steps performed in accordance with a preferred embodiment of the present invention.

FIG. 3 shows a schematic block diagram illustrating an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic block diagram illustrating a preferred embodiment of the present invention. In FIG. 1 is disclosed an implantable heart monitoring device for indicating congestive heart failure (CHF) comprising a processing means 2 and a sensing means 4 adapted to sense at least two heart events via at least one electrode lead 8, 10. In the figure an atrial lead 8 is provided with an electrode for sensing electrical heart signals in the right atrium and a ventricular lead 10 is provided with an electrode for sensing electrical heart signals in the right ventricle.

According to another preferred embodiment the heart events are sensed in the right and left ventricles.

According to still another preferred embodiment the heart events are sensed in the left atrium and in the right or left ventricles. A person skilled in the art is familiar to electrode leads specifically adapted for pacing and sensing in the left side of the heart, in particular via coronary sinus and the great veins of the heart. Therefore these types of leads will not be further described herein.

In most cases the heart event sensed in the right or left atrium is an intrinsic event but may also be a stimulated heart event.

The heart monitoring device may be any implantable heart stimulating device, e.g. a pacemaker, a cardioverter or a defibrillator.

The heart events are sensed, during one heart cycle, at different locations of the heart and signals related to the sensed events are applied to the processing means that determines at least one heart time interval between the sensed events in the same heart cycle. The processing means is then adapted to determine a congestive heart failure indicator value indicating the degree of CHF based upon a variability measure calculated from at least two heart time intervals from at least two heart cycles. The indicator value is determined in relation to previous indicator values. Preferably, the variability measure is calculated from at least two heart time intervals from consecutive heart cycles.

The variability measure may be any suitable parameter indicating the variability of the measured intervals. Among those is in particular preferred the standard deviation of the heart time intervals, the difference between heart time intervals, and the mean of the standard deviation of the heart time intervals.

According to an alternative embodiment of the present invention the congestive heart failure indicator value is determined from a combination of at least two different variability measures.

The variability measure calculation is based upon sensed heart event signals preferably obtained during a predetermined time period of 4-8 minutes measured at a regular basis, e.g. once a day.

Furthermore, the processing means includes a storage means 12 where the determined CHF indicator values are stored in order to be transmitted during a follow-up procedure to an external programming unit (not shown) for further analysis and display.

According to an alternative embodiment the sensed heart events are stored in the storage means 12 in order to be transmitted during a follow-up procedure to an external programming unit (not shown) where the CHF indicator value indicating the degree of CHF is determined at a later time.

FIG. 2 shows a flow chart illustrating essential steps performed in accordance with a preferred embodiment of the present invention. At least two heart events is sensed during the same heart cycle by the sensing means, preferably in the right atrium (RA) and in the right ventricle (RV). The sensed events are then identified and a heart time interval between the sensed events is determined. A congestive heart failure indicator value indicating the degree of CHF based upon a variability measure is calculated from at least two heart time intervals from at least two heart cycles. The indicator value is determined in relation to previous indicator values and is preferably stored in the storage means.

FIG. 3 shows a schematic block diagram illustrating an alternative embodiment of the present invention. In this embodiment the present invention is instead implemented in a conventional ECG equipment provided with extracorporeale surface electrodes. The signals sensed by the surface electrodes are applied to the sensing means provided with means for identifying the relevant heart events required to determine the heart time interval mentioned above in connection with the preferred embodiment described with references to FIG. 1. Also with regard to the processing it is referred to the above described preferred embodiment.

According to an alternative embodiment of the present invention also other time intervals may be used in order to establish the degree of CHF.

As most CHF patients receiving a biventricular pacing device have left bundle branch block (LBBB), there is a time interval from when the R wave reaches the right ventricular lead to when it reaches the left ventricular lead. This interval—called the RRRL interval—is also under autonomic control and may be used as the measured interval for the aforementioned device when determining a CHF indicator value. Measurement of the RRRL interval requires absence of pacing, which for some patients not is recommended, and this mode of operation may therefore be used only after careful considerations.

The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims. 

1-17. (canceled)
 18. A heart monitoring device for indicating congestive heart failure (CHF) comprising: a processor; a sensor combination configured to interact in vivo with a subject to sense at least two heart events during one heart cycle at different locations of the heart, and to emit respective sensor combination signals related to the at least two heart events; and said processor being in communication with said sensor combination and receiving said sensor combination signals therefrom, and said processor determining, from said sensor combination signals, at least one heart time interval between said at least two heart events in the same heart cycle, and determining a CHF indicator value representing a degree of CHF based on a variability measure calculated by the processor from at least two of said heart time intervals respectively determined from at least two different heart cycles, said processor determining said CHF indicator value in relation to at least one previous CHF indicator value.
 19. A heart monitoring device as claimed in claim 18 comprising an electronic cardiac therapy delivery system configured to deliver an electronic cardiac therapy to the heart, said processor controlling operation of said electronic cardiac therapy delivery system to adjust said electronic cardiac therapy dependent on said CHF indicator value.
 20. A heart monitoring device as claimed in claim 19 wherein said electronic cardiac therapy delivery system comprises a pulse generator selected from the group of pacing pulse generators, cardioverter pulse generators, and defibrillation pulse generators.
 21. A heart monitoring device as claimed in claim 18 wherein said sensor combination comprises a first sensor configured for placement in the right atrium of the heart to sense heart events in the right atrium, and a second sensor configured for placement in the right ventricle to sense heart events in the right ventricle.
 22. A heart monitoring device as claimed in claim 18 wherein said sensor combination comprises a first sensor configured for placement in the right ventricle of the heart to sense heart events in the right ventricle, and a second sensor configured for placement in the left ventricle to sense heart events in the left ventricle.
 23. A heart monitoring device as claimed in claim 18 wherein said sensor combination comprises a first sensor configured for placement in the left atrium of the heart to sense heart events in the left atrium, and a second sensor configured for placement in the left ventricle to sense heart events in the left ventricle.
 24. A heart monitoring device as claimed in claim 18 wherein said sensor combination comprises a first sensor configured for placement in the left atrium of the heart to sense heart events in the left atrium, and a second sensor configured for placement in the right ventricle to sense heart events in the right ventricle.
 25. A heart monitoring device as claimed in claim 18 wherein said processor determines said CHF indicator value based on the standard deviation of said at least tow heart time intervals, as said variability measure.
 26. A heart monitoring device as claimed in claim 18 wherein said processor determines said CHF indicator value based on the standard deviation of difference between said at least tow heart time intervals, as said variability measure.
 27. A heart monitoring device as claimed in claim 18 wherein said processor determines said CHF indicator value based on the mean of standard deviation of difference between said at least tow heart time intervals, as said variability measure.
 28. A heart monitoring device as claimed in claim 18 wherein said processor determines said CHF indicator value from a combination of at least two different variability measures.
 29. A heart monitoring device as claimed in claim 18 wherein said processor determines said variability measure from heart event signals sensed during a predetermined time period between four and eight minutes.
 30. A heart monitoring device as claimed in claim 18 comprising a pacing pulse delivery system configured to deliver pacing stimulation pulses at least to the right atrium of the heart, and wherein said sensor combination comprises a sensor that senses stimulated heart events I the right atrium as one of said at least two heart events.
 31. A heart monitoring device as claimed in claim 18 wherein said processor controls operation of said sensor combination to sense said at least two heart events on a regular basis.
 32. A heart monitoring device as claimed in claim 18 wherein said processor relates a magnitude of a currently calculated CHF indicator value to a magnitude of said at least one previous CHF indicator value.
 33. A heart monitoring device as claimed in claim 18 comprising a storage unit accessible by said processor, said processor storing each determined CHF indicator value in said storage unit, and said storage unit being extracorporeally accessible for readout of the CHF indicator values stored therein.
 34. A heart monitoring device as claimed in claim 18 comprising a storage unit accessible by said processor, said processor storing said at least two heart events represented in said sensor signals at a first point in time, and determining said CHF indicator value from the at least two heart events stored in said storage unit, at a second point in time that is non-contemporaneous with said first point in time.
 35. A heart monitoring device as claimed in claim 18 wherein said sensor combination comprises extracorporeal surface electrodes that sense said at least two heart events during one heart cycle. 